Use case: I want to have a backup of my “whole” system, i.e. nearly (ideally) all config and user’s data files, so I can easily restore it in case of a failure.

What I see: I don’t need to backup the distro’s file/rpm-ostree obviously. As that can easy be restored and then likely also all packages installed.

What I don’t know:
However, how to backup the data/config files of all apps and your own personal data?

The underlying issue may be that I can hardly install any command-line (backup) tools and set them up in a cron job or so. (Or can I?)

I’d e.g. like to setup borgbackup and with the “usual” Fedora/Linux packaging model that is easily possible, as it is in the Fedora packages.
However, how are we supposed to do this, if we have a read-only distro and can otherwise only install sandboxed software (as flatpaks)?

Note I’ve only tried out Silverblue for testing and read a bit about it and have not used it extensively.

One would hope that these proprietary programs are non-functional here.

One would hope I could install proprietary software on my Silverblue workstation / laptop as easily as I can install it on Fedora Workstation, Antergos Linux, Ubuntu 18.04 LTS or openSUSE Tumbleweed. Fedora doesn’t have to distribute encumbered software, but if they prevent me from using it I’ll switch to a distro that doesn’t.

I’m biased since I maintain it but I use BackupPC, it uses standard tools (typically rsync on *nix systems) and you can specify excludes to skip stuff that doesn’t matter like browser cache files. It also does compression and deduplication. I’ve got 1.75TB backed up but the whole system drive is only 1TB but it’s compressed/deduped to 150GB…

I knew about rclone - I used it as a replacement for the AWS CLI on a project last year. My personal requirement includes syncing with any Linux distro and Windows, and SpiderOak does that well for everything except Silverblue.

It turns out that my Office 365 Personal subscription includes a full terabyte of OneDrive space! I’ve only got about 50 GB on SpiderOak, but since I’m getting the OneDrive space free anyway I’m going to migrate to OneDrive via rclone, which will work on Silverblue. By the way, rclone does not support SpiderOak.